Photographic and image or information recording media require adequate lubrication for the purposes of transport through recording devices, imaging devices (camera, photofinishing, thermal head, etc.) and scratch protection. Also, backing layers on photographic negative film that can be used to magnetically record, and subsequently, to retrieve, information require excellent lubrication at their surface to improve the durability of the recording layer. Contact between the magnetic head and the outermost surface of the backing layers of the film is necessary, however, this imposes a great amount of stress to the backing layers and may result in rupture of the layer, and in loss of signal. Good lubrication allows for multiple transports of the film through various magnetic head-containing equipment. The lubricant must also remain effective after the film has been run through photographic processing solutions. The present invention provides low coefficient of friction and, in addition, provides durability for excellent performance under a magnetic head. The lubricant layer is transparent and does not interfere with the transmission of light through the photographic element.
There are many known lubricating agents. Some are not soluble, some are soluble in limited solvents which impose constraints and difficulties for the coating of these lubricants and on manufacturing. In addition, the solvents used as vehicles for the wax may attack or cause damage or undesirable changes in the surface of the layer or layers onto which the lube is being coated. In addition, these carrier solvents may not be environmentally friendly.
Photographic elements containing transparent magnetic oxide coatings on the side opposite the photographic emulsions have been well- documented. The need for lubricating layers on said magnetic oxide coatings have also been well-described. A variety of types of lubricants have been disclosed including fatty acids, fatty acid esters, silicones, waxes, etc. In general, the transparent magnetic layer and the lubricating layer are applied in separate coating steps. This reduces the manufacturing efficiency of the product by requiring several coating stations. Typically these layers have been applied by first coating a solution of the magnetic oxide layer onto a support using a bead coating technique. The coating is then dried and a lubricant layer is then coated over the magnetic layer using a similar technique. Thus, another disadvantage is that the lubricant containing layer is typically applied using a solvent as a carrier, thus, generating solvent and solvent vapor waste.
Alternatively, the lubricant can be added to the magnetic oxide coating solution such that both the magnetics and lubricant are coated simultaneously. This is advantageous because less coating stations are required, likely reducing waste and simplifying the production. Unfortunately, in order for the lubricant to be effective it must primarily reside at the uppermost surface of the dry coating. When the lubricant is added to the magnetic oxide solution, it is difficult for the lubricant to get to the surface. As the solution dries rapidly, the polymeric binder for the magnetic oxide will vitrify or solidify, which retards the mobility of the lubricant. Additionally, the lubricant may also go to the support/magnetics interface instead of the desired magnetics/air interface. The result is an improperly lubricated surface, or a coating with a high coefficient of friction.
Another drawback of adding the lubricant directly to the magnetics layer is that phase separation can occur resulting in a translucent or opaque film. The lubricant can destabilize the magnetics dispersion, resulting in flocculation of the particles. Also, the lubricant may not be compatible with the magnetics binder, which can lead to gross phase separation and loss of optical transparency. It is desired to have the lubricant phase separate and migrate to the air interface, without the loss of optical transparency. Obviously a very selective phase separation is desired and is difficult to control. Alternatively, the lubricant may not be soluble, or dispersible in the same solvents as are needed for the components of the transparent magnetic layer.
U.S. Pat. No. 5,807,661 describes the incorporation of sub-micron fluorinated ethylene polymers into the transparent magnetic layer on photographic film. These can be coated combined within the magnetic layer, or, as a separate layer over the magnetic layer. The advantage of the use of these microparticles of PTFE and FEP is that their use is adaptable to manufacturing since they can be dispersed into environmentally friendly solvents that are amenable to coating the magnetic layer, such as alcohols, ketones, acetates, and water. The problems, however, are that the particulate nature of the fluorinated ethylene polymers may lead to these particles being dislodged from the coating during the magnetic head wearing process thus creating dusting and magnetic head clogging, which are undesirable. Another problem that arises when the lubricant is combined with the magnetic layer prior to coating, not enough lubricant will get to the surface and lubrication will be inefficient and inadequate.
U.S. Pat. No. 3,954,637 (5/76), U.S. Pat. No. 3,998,989 (12/76), and U.S. Pat. No. 3,862,860 (1/75) by Pardee et al., Ball Brothers Research Corporation describe the use of a tetrafluoroethylene (TFE) telomer for improving lubricity and abrasion resistance of photographic film. The above components are dissolved in a solvent and cast as a continuous film. The tetrafluoroethylene telomer is only soluble in highly fluorinated solvents which are environmentally unfriendly and not acceptable for coating manufacture. The solvent listed is trichlorotrifluoroethane. Other solvents suggested in the patent for the TFE telomer are 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, chloroform, methylene chloride, carbon tetrachloride, dichloroethane, and dichloethylene. A TFE telomer is chemically different from high molecular weight polytetrafluoroethylene (PTFE) and has enhanced solubility over high molecular weight PTFE, such as that used in this invention. It is known that PTFE, FEP, and PFA polymers are not dissolvable in the above suggested solvents. "Polymer Handbook" third edition, J. Brandrup and E. H. Immergut, Eds., John Wiley & Sons, NY, 1989 (pages V-42, V-48, VII-385) states that PTFE and FEP and PFA are inert to essentially all common chemicals, and are only attacked by molten alkali metals, elemental fluorine, and pure oxygen at elevated temperatures. Sorption of solvents suggest that solutions of PTFE could be prepared in perfluorokerosene in the temperature range of 290-310.degree. C.]. Thus, a lubricant layer of the fluorinated polymer of the present invention can not be achieved as described in U.S. Pat. No. 3,954,637 (5/76), U.S. Pat. No. 3,998,989 (12/76), and U.S. Pat. No. 3,862,860 (1/75).
U.S. Pat. No. 5,294,525 suggests that fluorine type lubricants can be used for the magnetic layer on silver halide photographic element. These lubricants are included in an extensive list of all possible lubricants. The invention does not provide any direction on how to reduce to practice the use of fluorocarbon type polymers on photographic film and, as will be later shown, reduction to practice presents problems.
U.S. Pat. No. 4,863,762 describes a physical vapor deposition technique that deposits fluororesins onto a surface. However, in this process, there is a need to degrade the molecular weight of the initial resin sample prior to the vacuum deposition process. This is done by heating the resin in the presence of a fluorine source. It would be preferable if the use of highly undesirable fluorine gas were not necessary.
JP1251349 A (New Nippon Electric Co) discusses a Magneto-optical recording medium that comprises an optically transparent substrate onto which a magnetic film is formed. A macromolecular film formed by plasma polymerization of tetrafluoroethylene monomer is formed on the surface-side dielectric substance film.
Vacuum deposition of PTFE-like substances involve starting with gaseous monomers and doing a plasma polymerization.
Plasma assisted polymerization of fluorinated monomers is not a feasible approach for providing the necessary lubrication for the transparent magnetic layer of the film because it leads to the degradation of the transparent magnetic layer and an increase in the coefficient of friction COF. As demonstrated herein, the use of plasma to assist either the vacuum deposition of preformed PTFE or FEP, or the polymerization of fluorinated hydrocarbon monomers, leads to degradation of the transparent magnetic layer and an increase in the coefficient of friction COF.
Results hereinbelow demonstrate that a lubricating layer can not be prepared by plasma polymerization of fluorinated monomers, onto the transparent magnetic layer of a photographic element. Therefore, although the element might have been mentioned in U.S. Pat. No. 5,294,525 as an idea only, there is still needed in the art a way to form a lubricating layer of fluoropolymers on a transparent magnetic layer.